Resize all images in a folder using python and PIL.

resize-images.py

import os, sys
from PIL import Image

if __name__ == "__main__":
	fiList = os.listdir(sys.argv[1])
	fiList = fiList[:]
	fiList.sort()

	if len(sys.argv) < 3:
		print "Usage: {0} /src/folder /dest/folder [target-size]".format(sys.argv[0])
		exit()

	if sys.argv[1] == sys.argv[2]:
		print "Source and destination may not be the same"
		exit()

	targetSize = 1024. * 2.
	if len(sys.argv) >= 4:
		targetSize = float(sys.argv[3])

	for fi in fiList:

		fullFi = os.path.join(sys.argv[1],fi)
		outFullFi = os.path.join(sys.argv[2],fi)

		if not os.path.isfile(fullFi):
			continue

		print "in ", fullFi
		img = Image.open(fullFi)
		#print img.size

		scale1 = targetSize / img.size[0]
		scale2 = targetSize / img.size[1]
		scale = min(scale1, scale2)

		resizedDim = (img.size[0] * scale, img.size[1] * scale)
		resizedDim = map(round, resizedDim)
		resizedDim = map(int, resizedDim)

		rimg = img.resize(resizedDim)

		#print rimg.size
		print "out", outFullFi

		rimg.save(outFullFi)

After

img = Image.open(fullFi)

this 4 lines of code come handy if for png images

if img.mode in ('RGBA', 'LA'):
            background = Image.new(img.mode[:-1], img.size, '#fff')
            background.paste(img, img.split()[-1])
            img = background